The present invention relates to a process for producing fluoroolefins or fluorohaloolefins or fluorine-containing olefins, sometimes referred to hereinafter for convenience as fluoroolefins or fluorine-containing olefins, useful as intermediates for making industrial chemicals, in good yield, on an industrial scale and using commercially and readily available starting materials. More particularly, the present invention relates to a process for producing fluoroolefins, for example, 1,1,1,3,3-pentafluoropropene (also designated as xe2x80x9cHFC-1225zcxe2x80x9d), by the dehydrohalogenation of a halofluorocarbon, for example, 1-chloro-1,1,3,3,3-pentafluoropropane (also designated as xe2x80x9cHCFC-235faxe2x80x9d) which halofluorocarbon can be produced by photochlorinating 1,1,3,3,3-pentafluoropropane (also designated as xe2x80x9cHFC-245faxe2x80x9d).
The production of fluoroolefins such as CF3CHxe2x95x90CH2 by catalytic vapor phase fluorination of various saturated and unsaturated halogen-containing C3 compounds is described in U.S. Pat. Nos. 2,889,379; 4,798,818; and 4,465,786.
U.S. Pat. No. 5,532,419 discloses a vapor phase catalytic process for the preparation of fluorinated olefins using a chloro- or bromo-halofluorocarbon and HF.
EP 974571 discloses the preparation of 1,1,1,3-tetrafluoropropene by contacting 1,1,1,3,3-pentafluoropropane (HFC-245fa) with either an aqueous or alcoholic solution of KOH, NaOH, Ca(OH)2 or Mg(OH)2 or by contact of the HFC-245fa in the vapor phase with a chromium based catalyst at elevated temperature.
A. L. Henne et al., J.Am.Chem.Soc. (1946) 68, 496-497, describe the synthesis of various fluoroolefins from CF3CH2CF3 using, e.g., alcoholic KOH, with varying degrees of success. For example, it is stated that in some instances dehydrochlorination was unsuccessful, in another instance a protracted reaction time (three days) was required, or relatively low product yield (40%, 65%) was obtained.
P. Tarrant et al., J.Am.Chem.Soc. (1955), 77, 2783-2786, describe the synthesis of CF3CHxe2x95x90CF2 starting with: (1) 3-bromo-1,1,1,3,3-pentafluoropropane and reacting it with a hot solution of potassium hydroxide in water; and (2) 3-bromo-1,1,3,3-tetrafluoropropene and reacting it with HF at 150xc2x0 C. and neutralizing the reaction products with a potassium hydroxide solution.
Y. Kimura et al., J.Org.Chem. (1983), 48, 195-198, describe multiphase dehydrohalogenation of brominated compounds using aqueous potassium hydroxide and a phase transfer catalyst based on polyethylene glycols and polyethylene glycol-grafted copolymers. The authors note that poor results were obtained in the case of dehydrochlorination (page 197) and that C8 and C10 polyglycols having terminal hydroxyl groups were particularly effective compared to other phase transfer catalysts such as tetraalkylammonium salts, benzyltriethylammonium chloride and crown ethers. The authors also describe the selective activity for various phase transfer catalysts in particular reactions.
M. Halpern et al., J.Org.Chem. (1985), 50, 5088-5092, describe hydroxide ion (aqueous sodium hydroxide) initiated elimination of HCl and HBr from haloaromatic compounds using a quaternary ammonium salt phase transfer catalyst.
In view of the limited technology available to do so, it was desirable to develop an efficient, industrially acceptable method for producing fluoroolefins.
Process for the preparation of a fluoroolefin of the formula CF3CYxe2x95x90CXnHp wherein Y is a hydrogen atom or a halogen atom selected from the group consisting of fluorine, chlorine, bromine or iodine; X is a hydrogen atom or a halogen atom selected from the group consisting of fluorine, chlorine, bromine or iodine; n and p are integers independently equal to 0, 1 or 2, provided that (n+p)=2 comprising contacting, in the presence of a phase transfer catalyst: (A) a compound of the formula CF3C (R1aR2b)C(R3cR4d) wherein R1, R2, R3, and R4 are independently a hydrogen atom or a halogen selected from the group consisting of fluorine, chlorine, bromine and iodine, provided that at least one of R1, R2, R3, and R4 is halogen and there is at least one hydrogen and one halogen on adjacent carbon atoms; a and b are independently=0, 1 or 2 and (a+b)=2; and c and d are independently=0, 1, 2 or 3 and (c+d)=3; and (B) at least one alkali metal hydroxide. The compound of step (A) can be CF3CH2CF2H (a commercially available compound also known as HFC-245fa) or CF3CH2CF2Cl, a by-product from the manufacture of HFC-245fa.
The present invention can be generally described as a process for the preparation of fluoroolefins of the formula CF3CYxe2x95x90CXnHp wherein Y is a hydrogen atom or a halogen atom selected from the group consisting of fluorine, chlorine, bromine or iodine; X is a hydrogen atom or a halogen atom selected from the group consisting of fluorine, chlorine, bromine or iodine; n and p are integers independently equal to 0, 1 or 2, provided that (n+p)=2, comprising contacting, in the presence of a phase transfer catalyst: (A) a compound of the formula CF3C (R1aR2b)C(R3cR4d) wherein R1, R2, R3, and R4 are independently a hydrogen atom or a halogen selected from the group consisting of fluorine, chlorine, bromine and iodine, provided that at least one of R1, R2, R3, and R4 is halogen; a and b are independently=0, 1 or 2 and (a+b)=2; and c and d are independently=0, 1, 2 or 3 and (c+d)=3; and (B) at least one alkali metal hydroxide.
Fluoroolefins are produced by the process of the present invention by dehydrohalogenating, in the presence of a phase transfer catalyst, a compound of formula (I) comprising contacting the compound of formula (I) with at least one alkali metal hydroxide:
CF3C(R1aR2b)C(R3cR4d)xe2x80x83xe2x80x83(I)
wherein R1, R2, R3, and R4 are independently a hydrogen atom or a halogen selected from the group consisting of fluorine, chlorine, bromine and iodine, provided that at least one of R1, R2, R3, and R4 is halogen and there is at least one hydrogen and one halogen on adjacent carbon atoms; a and b are independently=0, 1 or 2 and (a+b)=2; and c and d are independently=0, 1, 2 or 3 and (c+d)=3. Included among the compounds of formula (I) that can be used in the present invention is 1,1,1,3,3-pentafluoropropane or HFC-245fa. Various methods for producing this material are described in U.S. Pat. Nos. 5,710,352; 5,969,198; and 6,023,004. Another method described in U.S. Pat. No. 5,728,904 is said to be economical, amenable to large scale application and uses readily available raw materials. The process of that patent uses three steps, as follows: 1) formation of CCl3CH2CCl3 by the reaction of CCl4 with vinylidene chloride; 2) conversion of CCl3CH2CCl3 to CF3CH2CF2Cl by reaction with HF in the presence of a fluorination catalyst, selected from TiCl4, SnCl4 or mixtures thereof; and 3) reduction of CF3CH2CF2Cl to CF3CH2CF2H. Since both CF3CH2CF2H and CF3CH2CF2Cl are useful in the present invention for producing a fluoroolefin, the described process can be utilized to obtain alternative starting materials. Furthermore, commercial quantities of CF3CH2CF2H, also known as HFC-245fa, are available from Honeywell International Inc., Morristown, N.J. for use as the starting material of the present process for direct conversion to the olefin CF3CHxe2x95x90CFH by dehydrofluorination according to the process disclosed herein. Other useful starting materials for the production of fluoroolefins and/or fluorohaloolefins include the following: CF3CH2CF2Br; CF3CH2CF2I; CF3CHFCF2Br; CF3CH2CH2Cl; CF3CH2CH2Br; CF3CH2CH2I; CF3CHBrCF2Br; CF3CHClCF2Cl; CF3CH2CFHCl; CF3CH2CFHBr; CF3CHClCF2H; CF3CH2CCl3; CF3CH2CF3; and the like.
In order to carry out the dehydrohalogenation process step of the present invention there is employed at least one alkali metal hydroxide. The alkali metal is selected from the group consisting of the metals of Group 1 of the Periodic Table of the Elements as shown in Hawley""s Condensed Chemical Dictionary, 13th Edition, 1997. Reference to xe2x80x9cgroupsxe2x80x9d in this table is made according to the xe2x80x9cNew Notationxe2x80x9d. Preferably the alkali metal is selected from the group consisting of lithium, sodium and potassium; more preferably, sodium and potassium; most preferably, potassium. Useful concentrations of the hydroxide are from about 1 to about 50 wt. %; preferably from about 5 to about 30 wt. %; most preferably from about 10 to about 30 wt. %. While it is possible to use hydroxides other than alkali metal hydroxides, they tend to be less soluble, particular in aqueous systems and are therefore less desirable. For example, hydroxides of the Group 2 metals (e.g., Ca, Mg, and Ba) are of this type; such as magnesium hydroxide. In carrying out the process, the molar ratio of hydroxide, preferably alkali metal hydroxide, relative to the amount of CF3C(R1aR2b)C(R3cR4d) is from about 1 to about 20; preferably from about 1 to about 15; more preferably from about 1 to about 12; for example, from about 1 to about 10.
The dehydrohalogenation reaction can be accomplished using an aqueous solution of at least one alkali metal hydroxide, without the need for additional solvent or diluent, other than the water present as a consequence of using aqueous base or alkali metal hydroxide. However, a solvent or diluent can be used if desired for convenience in carrying out the process, e.g., to modify the system viscosity, to act as a preferred phase for reaction by-products, or to increase thermal mass, etc. Useful solvents or diluents include those that are not reactive with or negatively impact the equilibrium or kinetics of the process and include alcohols such as methanol and ethanol; ethers such as diethyl ether, dibutyl ether; esters such as methyl acetate, ethyl acetate and the like; linear, branched and cyclic alkanes such as cyclohexane, methylcyclohexane; fluorinated diluents such as perfluoroisopropanol, perfluorotetrahydrofuran; chlorofluorocarbons such as CFCl2CF2Cl, etc.
The dehydrohalogenation reaction is conveniently and preferably conducted in the presence of a phase transfer catalyst. For purposes of the present invention, a phase transfer catalyst is a substance that facilitates the transfer of ionic compounds (e.g., reactants or components) into an organic phase from, e.g., a water phase. In the present invention, an aqueous or inorganic phase is present as a consequence of the alkali metal hydroxide and an organic phase is present as a result of the fluorocarbon. The phase transfer catalyst facilitates the reaction of these dissimilar and incompatible components. While various phase transfer catalysts may function in different ways, their mechanism of action is not determinative of their utility in the present invention provided that the phase transfer catalyst facilitates the dehydrohalogenation reaction based on the identified reactants. The phase transfer catalyst can be ionic or neutral and is selected from the group consisting of crown ethers, onium salts, cryptates and polyalkylene glycols and derivatives thereof. An effective amount of the phase transfer catalyst should be used in order to effect the desired reaction; such an amount can be determined by limited experimentation once the reactants, process conditions and phase transfer catalyst are selected. Typically, the amount of catalyst used relative to the amount of CF3C(R1aR2b)C(R3cR4d) present is from about 0.001 to about 10 mol %; for example from about 0.01 to about 5 mol %; alternatively, for example from about 0.05 to about 5 mol %
Crown ethers are cyclic molecules in which ether groups are connected by dimethylene linkages; the compounds form a molecular structure that is believed to be capable of xe2x80x9creceivingxe2x80x9d or holding the alkali metal ion of the hydroxide and to thereby facilitate the reaction. Particularly useful crown ethers include 18-crown-6, especially in combination with potassium hydroxide; 15-crown-5, especially in combination with sodium hydroxide; 12-crown-4, especially in combination with lithium hydroxide. Derivatives of the above crown ethers are also useful, e.g., dibenzo-18-crown-6, dicyclohexano-18-crown-6, and dibenzo-24-crown-8 as well as 12-crown-4. Other polyethers particularly useful for alkali metal compounds, and especially for lithium, are described in U.S. Pat. No. 4,560,759 which is incorporated herein by reference to the extent permitted. Other compounds analogous to the crown ethers and useful for the same purpose are compounds which differ by the replacement of one or more of the oxygen atoms by other kinds of donor atoms, particularly N or S, such as hexamethyl-[14]-4,11-dieneN4.
Onium salts include quaternary phosphonium salts and quaternary ammonium salts that may be used as the phase transfer catalyst in the process of the present invention; such compounds can be represented by the following formulas II and III:
R1 R2 R3 R4 P(+) Xxe2x80x2(xe2x88x92)xe2x80x83xe2x80x83(II)
R1 R2 R3 R4 N(+) Xxe2x80x2(xe2x88x92)xe2x80x83xe2x80x83(III)
wherein each of R1, R2, R3 and R4, which may be the same or different, is an alkyl group, an aryl group or an aralkyl group, and Xxe2x80x2 is a halogen atom. Specific examples of these compounds include tetramethylammonium chloride, tetramethylammonium bromide, benzyltriethylammonium chloride, methyltrioctylammonium chloride (available commercially under the brands Aliquat 336 and Adogen 464), tetra-n-butylammonium chloride, tetra-n-butylammonium bromide, tetra-n-butylammonium hydrogen sulfate, tetra-n-butylphosphonium chloride, tetraphenylphosphonium bromide, tetraphenylphosphonium chloride, triphenylmethylphosphonium bromide and triphenylmethylphosphonium chloride. Among them, benzyltriethylammonium chloride is preferred for use under strongly basic conditions. Other useful compounds within this class of compounds include those exhibiting high temperature stabilities (e.g., up to about 200xc2x0 C.) and including 4-dialkylaminopyridinium salts such as tetraphenylarsonium chloride, bis[tris(dimethylamino)phosphine]iminium chloride and tetratris[tris(dimethylamino)phosphinimino]phosphonium chloride; the latter two compounds are also reported to be stable in the presence of hot, concentrated sodium hydroxide and, therefore, can be particularly useful.
Polyalkylene glycol compounds useful as phase transfer catalysts can be represented by the formula:
R6O(R5O)tR7xe2x80x83xe2x80x83(IV)
wherein R5 is an alkylene group, each of R6 and R7, which may be the same or different, is a hydrogen atom, an alkyl group, an aryl group or, an aralkyl group, and t is an integer of at least 2. Such compounds include, for example glycols such as diethylene glycol, triethylenre glycol, tetraethylene glycol, pentaethylene glycol, hexaethylene glycol, diisopropylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol and tetramethylene glycol, and monoalkyl ethers such as monomethyl, monoethyl, monopropyl and monobutyl ethers of such glycols, dialkyl ethers such as tetraethylene glycol dimethyl ether and pentaethylene glycol dimethyl ether, phenyl ethers, benzyl ethers, and polyalkylene glycols such as polyethylene glycol (average molecular weight about 300) dimethyl ether, polyethylene glycol (average molecular weight about 300) dibutyl ether, and polyethylene glycol (average molecular weight about 400) dimethyl ether. Among them, compounds wherein both R6 and R7 are alkyl groups, aryl groups or aralkyl groups are preferred.
Cryptates are another class of compounds useful in the present as phase transfer catalysts. These are three-dimensional polymacrocyclic chelating agents that are formed by joining bridgehead structures with chains that contain properly spaced donor atoms. For example, bicyclic molecules that result from joining nitrogen bridgeheads with chains of (xe2x80x94OCH2CH2xe2x80x94) groups as in 2.2.2-cryptate (4,7,13,16,21,24-hexaoxa-1,10-diasabicyclo-(8.8.8)hexacosane; available under the brand names ryptand 222 and Kryptofix 222). The donor atoms of the bridges may all be O, N, or S, or the compounds may be mixed donor macrocycles in which the bridge strands contain combinations of such donor atoms.
Combinations of phase transfer catalysts from within one of the groups described above may also be useful as well as combinations or mixtures from more than one group, for example, crown ethers and oniums, or from more than two of the groups, e.g., quaternary phosphonium salts and quaternary ammonium salts, and crown ethers and polyalkylene glycols.
The reaction is conducted usually at a temperature within the range of from about 0xc2x0 C. or slightly above to about 80xc2x0 C., preferably from about 0xc2x0 C. or slightly above to about 60xc2x0 C., more preferably from about 0xc2x0 C. or slightly above to about 40xc2x0 C.; for example from about 0xc2x0 C. to about 25xc2x0 C. Reference to xe2x80x9cslightly abovexe2x80x9d is intended to mean in the range of from about 1 to about 5xc2x0 C. and temperatures therein between. Under process conditions where freezing of the diluent, solvent or reactants is not a factor, temperatures below 0xc2x0 C. can be used, for example from about xe2x88x9220xc2x0 C. to about 80xc2x0 C.; preferably from about xe2x88x9210xc2x0 C. to about 60xc2x0 C.; more preferably from about xe2x88x925xc2x0 C. to about 40xc2x0 C.
While there is no particular restriction as to the reaction pressure, in other words the reaction may be conducted under atmospheric pressure or under an elevated pressure, it may be necessary to operate at elevated pressure if it is desired to maintain the fluorocarbon starting material and the fluoroolefin in the liquid state, at least during the reaction. When the reaction is conducted under elevated pressure, useful pressures are from about 1 to about 5 atmospheres (about 100 kPa to about 500 kPa). The reaction time can vary in accordance with the starting compound CF3C(R1aR2b)C(R3cR4d), as well as the reaction temperature selected and the yield or conversion desired. For example, typically reaction times for reactions conducted at from about 0xc2x0 C. to about 65xc2x0 C., preferably from about 0 to about 25xc2x0 C., can vary from about 0.1 to about 20 hours; preferably from about 0.1 to about 2.0 hours.
The process described herein is useful for the preparation of fluoroolefins and/or fluorohlaloolefins having the following formula:
CF3CYxe2x95x90CXnHpxe2x80x83xe2x80x83(V)
wherein Y is a hydrogen atom or a halogen atom selected from the group consisting of fluorine, chlorine, bromine or iodine; X is a hydrogen atom or a halogen atom selected from the group consisting of fluorine, chlorine, bromine or iodine; n and p are integers independently equal to 0, 1 or 2, provided that (n+p)=2. Such compounds include CF3CHxe2x95x90CF2, CF3CHxe2x95x90CFH, CF3CBrxe2x95x90CF2, CF3CHxe2x95x90CH2, CF3CF=CF2, CF3CCl=CF2, CF3CHxe2x95x90CHCl, CF3CClxe2x95x90CHF, CF3CHxe2x95x90CCl2, CF3CFxe2x95x90CCl2, and the like. The fluorine-containing olefins prepared by the method of this invention are readily removed from the reaction mixture and/or solvent or diluent by phase separation. Depending on the extent of conversion of the starting material, the product can be used directly or further purified by standard distillation techniques.
The fluoroolefins obtained by the process of the present invention are useful as monomers for producing fluorine-containing oligomers, homopolymers and copolymers as well as intermediates for other fluorine-containing industrial chemicals.
All references herein to elements or metals belonging to a certain Group refer to the Periodic Table of the Elements as it appears in Hawley""s Condensed Chemical Dictionary, 13th Edition. Also, any references to the Group or Groups shall be to the Group or Groups as reflected in this Periodic Table of Elements using the xe2x80x9cNew Notationxe2x80x9d system for numbering groups.
The following examples are given as specific illustrations of the invention. It should be understood, however, that the invention is not limited to the specific details set forth in the examples. All parts and percentages in the examples, as well as in the remainder of the specification, are by weight unless otherwise specified.
Further, any range of numbers recited in the specification or paragraphs hereinafter describing or claiming various aspects of the invention, such as that representing a particular set of properties, units of measure, conditions, physical states or percentages, is intended to literally incorporate expressly herein by reference or otherwise, any number falling within such range, including any subset of numbers or ranges subsumed within any range so recited. The term xe2x80x9caboutxe2x80x9d when used as a modifier for, or in conjunction with, a variable, is intended to convey that the numbers and ranges disclosed herein are flexible and that practice of the present invention by those skilled in the art using temperatures, concentrations, amounts, contents, carbon numbers, and properties that are outside of the range or different from a single value, will achieve the desired result, namely, processes for the preparation of fluoroolefins and reactants used in such processes.